A visitor of the values of annotation type elements, using a variant of the visitor design pattern. Unlike a standard visitor which dispatches based on the concrete type of a member of a type hierarchy, this visitor dispatches based on the type of data stored; there are no distinct subclasses for storing, for example,
values. Classes implementing this interface are used to operate on a value when the type of that value is unknown at compile time. When a visitor is passed to a value's
method applicable to that value is invoked.
Classes implementing this interface may or may not throw a
NullPointerException if the additional parameter
null; see documentation of the implementing class for details.
WARNING: It is possible that methods will be added to this interface to accommodate new, currently unknown, language structures added to future versions of the Java™ programming language. Therefore, visitor classes directly implementing this interface may be source incompatible with future versions of the platform. To avoid this source incompatibility, visitor implementations are encouraged to instead extend the appropriate abstract visitor class that implements this interface. However, an API should generally use this visitor interface as the type for parameters, return type, etc. rather than one of the abstract classes.
Note that methods to accommodate new language constructs could be added in a source compatible way if they were added as default methods . However, default methods are only available on Java SE 8 and higher releases and the
javax.lang.model.* packages bundled in Java SE 8 were required to also be runnable on Java SE 7. Therefore, default methods were not used when extending
javax.lang.model.* to cover Java SE 8 language features. However, default methods are used in subsequent revisions of the
javax.lang.model.* packages that are only required to run on Java SE 8 and higher platform versions.